Melt spinning of synthetic yarns

ABSTRACT

An apparatus for melt spinning of polymers into synthetic yarns having greater bundle uniformity has a spinning assembly for extruding molten polymers through orifices in a spinning plate to form filaments and a blow box for directing cooling gas transversely across and through the filaments that extend vertically downwardly from the spinning plates. The spinning plate is provided with at least two groups of orifices and the groups are arranged to provide one or more open lanes or channels that extend across the plate in a direction parallel to the direction of flow of the cooling gas. This lane has a width greater than the distance between adjacent orifices.

This invention relates to an improved apparatus for the manufacture ofsynthetic yarns by melt spinning and, in particular, to an apparatus formelt spinning of multi-filament yarns having a spinneret with orificesarranged in a pattern that produces yarns of low denier per filamentcount having highly uniform deniers and the process for producing suchyarns with this apparatus.

During the production of synthetic yarns from polymeric materials suchas the polyesters and nylons by melt spinning, it is conventional toextrude the polymeric material downwardly through a spinneret plate andto cool the resulting filaments by passing air transversely to thedirection of the travel of the filaments exiting from the spinneret.Also, it has been proposed to arrange the spinning orifices in thespinneret in a pattern or configuration to reduce variations in thecooling rate of the filaments.

Generally, these earlier attempts to improve the uniformity in thecooling of the initially formed filaments involve the use of arelatively small number of spinning orifices in a particularconfiguration in the spinneret plate or the use of a spinneret platewhich is relatively large so as to provide a greater spacing betweenadjacent spinning orifices which consequently provides a greater spacebetween the individual filaments, and thus promotes more uniform coolingof the filaments as the air or other gas is transversely passed throughthe bundle of filaments exiting from the spinneret.

For example, U.S. Pat. No. 3,335,210 to Vinicki discloses a method forspinning filament yarns wherein a plurality of filaments is extrudedthrough a spinneret plate having openings arranged in a "V"configuration, the "V" formation of filaments is passed through a quenchregion and a stream of air is directed under pressure at an angleperpendicular to the filaments and into the mouth of the "V" in thequench region so that the filaments produce a funneling of the airstream towards the apex of the "V" formation.

U.S. Pat. No. 2,969,561 describes a spinneret pack assembly having aspinneret plate with at least forty orifices arranged in a substantiallyrectangular pattern with a length of at least three times its width. Theorifices are staggered in the direction of the width, and are inrelatively long rows that are spaced relatively far apart. The orificesare spaced at least 0.15 inches apart.

The patent to Bruni (U.S. Pat. No. 3,293,696) discloses anotherspinneret for melt-spinning synthetic polymers wherein the orifices inthe spinneret are arranged in two converging rows which include an angletherebetween with the distance between any two adjacent orifices ineither of the rows being such that the projections of the centers ofthese two orifices to a line perpendicular to the direction of an airstream passing transversely to the filaments is at least 1 millimeter,and the rows are so disposed that a line bisecting the angle is parallelto the direction of the stream.

Another pattern for facilitating the production of synthetic filamentsis shown in U.S. Pat. No. 3,100,675. The spinning orifices in thespinning plate disclosed in this patent are arranged in rows parallel toeach other, and in a straight line in each row. The distance between theorifices are equal in all rows and usually at least about 5.5millimeter. As shown in FIG. 4 of this patent the gaseous cooling mediumflows parallel to the rows of orifices as indicated by the arrow.

In each of the spinning devices shown in these patents, a relativelysmall number of spinning orifices are provided per unit area of thespinneret, and consequently the air stream has little difficulty inuniformly cooling the filaments extruded through the orifices.

However, it has been found that during the production of syntheticyarns, such as polyester yarns, having a denier of 150 and consisting of96 filaments, that a very high unevenness, i.e. denier non-uniformity,occurs with a spinneret having a cluster pattern conventionally used inthe spinning of yarns. Such a conventional pattern is illustrated inFIG. 9 of the patent to Viniki.

In accordance with this invention an apparatus is provided whichovercomes the disadvantages of the prior art and which ensures a muchmore uniform denier of the bundle of filaments produced from a spinneretplate having a high orifice density. It will be understood that theexpression "high orifice density" means that a spinning plate having arelatively small diameter will have a large number of spinning orificestherein. For example, a plate with a diameter on the order of 60millimeters will have from 48 to 96 or more spinning orifices providedtherein, with each orifice having a diameter ranging from about 200 to300μ.

More particularly, it has been found that spinneret plates with thespinning orifices or holes arranged in patterns having one or more airchannels or lanes extending across the spinneret plate will reduce theunevenness of the denier in the filaments substantially.

Thus, this invention is directed to an apparatus for melt spinning ofsynthetic yarns including a spinneret assembly means for extrudingmolten polymeric material through spinning orifices in a plate and ablow box assembly for directing a cooling gas transversely across thefilaments which are extruded vertically down from the spinning plate,the spinning plate having at least two groups of a plurality of spinningorifices which are spaced apart, with the groups being arranged toprovide at least one open lane or channel between adjacent groups. Thelane or channel has a length that is sufficient to extend across theportion of the plate having the orifices provided therein and has awidth that is greater than the distance between adjacent spinningorifices within each of the groups.

Furthermore, it has been found that the groups of orifices are arrangedso that the open lane or channel is preferably arranged parallel to thedirection of flow of the cooling gas through the filaments and acrossthe spinneret plate. This arrangement promotes the penetration of thecooling gas between and around the groups of filaments which extendvertically downward from the spinneret plate. Consequently, the denierof the filament clusters or bundles are more even along the length ofyarn. It will also be appreciated that it is advantageous to arrange theorifices in each group in rows which also extend parallel to thedirection of flow of the cooling gas, and that the number of open lanesor channels provided on the spinneret plate may be varied. Generally,from 1 to 5 channels are provided, with each channel being preferablyparallel to the other.

In accordance with this invention, a group of orifices comprises atleast two rows of spaced orifices, preferably the rows are parallel. Theorifices are usually spaced apart at a distance of at least 1 to 2 mm.in order to ensure sufficient space between filaments exiting thespinneret in the resulting yarn or filament cluster.

The shape of the orifices through which the polymer melt is extruded maybe varied and includes any shape of orifice. Circular and odd-shapedorifices such as those used to produce a multilobal yarn, for example atrilobal yarn, may be used in accordance with the present invention. Thediameter of circular spinning orifices may vary from about 175 to 450microns.

This invention is particularly directed to an apparatus for producingmulti-filament yarns having a high filament count and a low denier perfilament count on existing melt spinning apparatus which isconventionally used to produce yarns with lower filament counts. In suchapparatus, the spinneret assemblies will have a spinning plate with adiameter of from 20 to 200 mm. For example, a conventional spinningplate may have a diameter of 40 mm. and contain 24 orifices or holesarranged in a cluster with the holes being spaced in a pre-selecteddistance apart in rows which are spaced at the same or anotherpre-selected distance apart. It will be appreciated that in such knownspinneret assemblies the row of holes for forming a cluster may bespaced at distances on the order of 5 mm. and the orifices in each rowmay be spaced at distances on the order of 7 mm., and therefore thedensity of the filament cluster or bundle vertically extending down fromthe plate is relatively low. In such situations, the cooling gas usuallyhas ample space around each of the filaments to penetrate into thefilament cluster and promote uniform cooling of the filaments. However,when the number of orifices or holes is substantially increased thedensity of the filaments within the cluster rapidly increases and insuch cases the instability of the thread line as widened by its lateralmotion is increased. For example, it has been found that when arelatively high filament count is required in a low denier yarn, such asin the production of polyester yarns having 96 filaments and a denier of150, the degree of unevenness of the filaments within the yarn is on theorder of from 10 to 12%. Advantageously, in accordance with the presentinvention this degree of unevenness is reduced to be on the order offrom 4 to 6% while still maintaining the same filament count and thesame low denier and using the same size spinning plate. For example, aspinning plate in accordance with the present invention may have adiameter of 60 mm. and can be provided with from 48 to 96 orifices toproduce yarns having a total denier of from 70 to 150.

As heretofore noted, the width of the open lanes or channels, that isthe distance between adjacent groups of orifices in accordance with thisinvention, is significantly larger than the distance between adjacentrows of orifices within a group. For example, in a 60 mm. spinning platean open lane will have a width in the range of from 1.5 to 10 times thespacing between the rows within a group. This spacing may be defined bythe following, that is

    1.5≦W.sub.1 /W.sub. r≦ 10.0

wherein W₁ is the width of a lane and W_(r) is the distance between rowsof orifices.

The quantity W₁ /W_(r) can be referred to as a "normalized lane width".

In accordance with the present invention the normalized lane width hasan effective range which will be expected to change with the length ofthe lane, that is the centerline distance from the entrance end to theexit end of the lane extending across the spinneret plate. In general,the longer the lane the effective range of the normalized lane widthwill increase; whereas the shorter the lane, the effective range of thenormalized lane width will decrease.

This invention is also directed to a process for producing yarns whichcomprises extruding a molten polymeric material through a spinning platehaving a plurality of orifices to form a plurality of filaments,arranging the filaments into a plurality of groups by providing thespinning plate with at least one open lane that is free of orifices andthat extends across the spinning plate between groups of orificescorresponding to the groups of filaments, the orifices being arranged inparallel rows within each group and the lane having a width greater thanthe distance between adjacent rows, and passing a cooling gastransversely across the filaments, in a direction parallel to a centerline of the lane to promote uniform cooling of the filaments.

The apparatus of this invention will be better understood from thefollowing detailed description taken in connection with the accompanyingdrawing in which:

FIG. 1 is a side elevational view of the melt spinning apparatus of theinvention;

FIG. 2 is a front elevational view partly in section of the apparatus ofFIG. 1;

FIG. 3 through FIG. 7 are bottom views of a spinning plate having atleast one open lane or channel according to this invention; and FIGS. 8,9 and 10 are bottom views of spinning plates having orifices arranged ina conventional-type pattern wherein the orifices are grouped together.

In FIG. 1 reference numeral 1 denotes a spinneret assembly from which amolten polymeric material is extruded in a known manner through officesin a pair of spinning plates 2. A blow box assembly is indicatedgenerally by reference numeral 3 and is divided into compartments 4 and5, an inclined end wall 6 connects sidewalls 8 and 9 of the compartments4 and 5 and an intermediate wall 10 extends parallel to the sidewalls 8and 9 and separates the compartments 4 and 5. This wall is secured withend wall 6. A gas filter in the form of a wire screen 11 is provided ineach compartment 4 and 5 upstream of the spinning plate and serves toquiet the cooling gas before it passes over the filaments 12 extrudeddownwardly from the spinning plates.

The cooling gas such as air is supplied to each of the compartments 4and 5 from the bottom thereof. This air is supplied under a slightpressure in order that it may have the required flow rate of from about80 to greater than 250 cubic ft./min. The filter 11 diffuses the air asit enters each of the compartments and thereby tends to reduceturbulence. It will be understood that in accordance with conventionalprocedures the air cools the yarn formed during the spinning operationand carries any vaporous materials out of each of the compartments intothe atmosphere or into a collecting duct.

The filaments extruded from plates 2 have been shown by a number oflines in FIGS. 1 and 2, it being understood that a larger number offilaments are being formed. Also, one open lane 13 is shown between twoadjacent groups of filaments, with the width of the lane being enlargedto facilitate illustration.

In FIG. 3 there is illustrated an embodiment of a spinning plate 2having 96 orifices and one open lane 13 provided between the two groupsof orifices 14. FIGS. 4 and 5 respectively show spinning plates having96 orifices and having three and five open lanes that extend parallel toeach other and parallel to the rows of orifices in each group oforifices.

In the spinning plate in FIG. 6 there are 48 orifices arranged toprovide three open lanes; whereas FIG. 7 shows a 64 orifice plate withthree open lanes. It will be understood that the arrows at the top ofeach of the FIGS. 3 to 10 represent the direction of flow of the coolinggas across the spinning plates.

Also in FIG. 3, the length of the open lane is designated by center line15 and the width by the distance W₁, with the spacing between adjacentrows of orifices being the distance W_(r).

It will be understood that the orifices 14 are conventional orifices andin the embodiments shown and in the examples that follow each orificehas a wide cylindrical portion extending from the upper surface of theplate in contact with the molten polymer, an intermediate conicallytapered portion and a narrow cylindrical portion that extends to thebottom surface of the plate.

Also in the process of this invention various polymeric materialsconventionally used to produce filaments by melt spinning may beemployed; for example polyamides, polyesters, polyethers, polyacetals,polyolefins, vinyl polymers and the like.

Furthermore, the extrusion temperature and the extrusion rates of themolten polymeric material are conventional and are determined by theparticular polymer being used and the deniers of the desired yarnproducts.

The winding speeds used to take up the filaments may vary from 600 to2,000 meters per minute (mpm) or more with drawing speeds of from 500 to1,000 mpm.

This invention will be further illustrated by the following exampleswherein polyester yarns are produced with deniers ranging from about 70to about 150.

EXAMPLE 1

Granular polyethylene terephthalate having an intrinsic viscosity of0.64 and a moisture content of less than 0.01% by weight was melted andspun into yarn using an electrically heated extruder at 290° C. with apumpblock heated by a gaseous medium at 295° C. The molten polymer wasforced at 2,300 psi through the 96 orifices in a 60 mm. diameterspinneret similar to that shown in FIG. 4 having three open lanes. Theorifices had a diameter of 200 microns and were spaced into four groups.The orifices within each group were arranged into rows parallel to thedirection of air flow. The distance between the outer row of an innergroup of orifices and the inner row of the adjacent outer group oforifices was 6.0 mm. The distance between the inner row of an innergroup of orifices and the inner row of the other inner group of orificeswas 8 mm. Adjacent rows of orifices within a group were spaced 2.0 mm.apart. Within a row, the orifices were spaced 5.0 mm., apart. Within agroup, orifices in a given row were displaced relative to the orificesin an adjacent row by half the distance separating the orifices within arow.

During the spinning, the lower surface of the spinning plate had atemperature of 276° C. positioned below the spinneret plate was aconventional blow box assembly. Air at room temperature was passedthrough the blow box rear chamber. The air moved through the blow boxtransversely to the molten filaments falling downwardly through the sameand flowed parallel to the rows of orifices. The velocity of the air was34 centimeters per second and the zone through which the filaments wereexposed to the air was 100 centimeters in length. The quantity of theair was 2275 liters per minute. The resulting threads were wound at 1400mpm and subsequently stretched to a total denier of 149.5 with anaverage filament denier of 1.56. The denier evenness was 6.2%, asdetermined by a standard test for evenness of textile strands, ASTMD1425-67 using a Uster tester (Type GGP-C10).

EXAMPLE 2

Additional polymer was spun in an identical manner to Example 1 except aconventional spinning plate of the same diameter was used in which theorifices were all arranged into a single group positioned on the cornersof 3.7 mm. squares as shown in FIG. 10. The resultant threads had adenier evenness of 11.0%.

EXAMPLES 3 and 4

Additional polyester polymer was spun under similar conditions using aspinning plate having one lane as shown in FIG. 1 or two lanes (notshown) with 96 orifices arranged in two or three groups. Each orificehad a diameter of 200μ . With the single lane the resultant threads hada denier evenness of from 7-8%; whereas with the two lanes the threadshad a denier evenness of from 5% to 7.5%.

EXAMPLES 5

Granular polyethylene terephthalate having an intrinsic viscosity of0.64 and a moisture content of less than 0.01% by weight was melted andspun into yarn using electrically heated extruder at 290° C. with apumpblock heated by a gaseous medium at 295° C. The molten polymer wasforced through the 96 orifices in a spinning plate having a diameter of60 mm. and the orifices arranged as shown in FIG. 5. The orifices had adiameter of 200 microns and were spaced into six groups. The orificeswithin each group of orifices were arranged into rows parallel to theair flow. The distance between the rows of adjacent groups of orificeswas 6.0 mm. Adjacent rows of orifices within a group of orifices werespaced 2.0 mm. apart.

During the spinning, the lower surface of the spinning plate had atemperature of 276° C. Positioned below the spinneret plate was a blowbox assembly. Air at room temperature was passed through the blow boxrear chamber. The air moved through the blow box transversely to themolten filaments falling downwardly through the same and flowed parallelto the rows of orifices. The qunatity of the air was 3450 liters perminute. The resulting threads were wound at 1000 mpm and subsequentlydrawn into a yarn having an average filament denier of 1.56. The denierevenness was 6%.

EXAMPLE 6

Additional polymer was spun in an identical manner to Example 5 with a60 mm. diameter plate except the orifices were all arranged into asingle group of uniformly spaced orifices positioned on the corners of a3.7 mm. square (FIG. 10). The resultant threads had a denier evenness of8.9%.

EXAMPLE 7

Granular polyethylene terephthalate having an intrinsic ciscosity of0.64 and a moisture content of less than 0.01% by weight was melted andspun into yarn using electrically heated extruder at 290° C. with apumpblock heated by a gaseous medium at 295° C. The molten polymer wasforced through the 64 orifices in the spinning plate having a diameterof 60 mm. and the orifices arranged as shown in FIG. 7. The orifices hada diameter of 200 microns and were spaced into four groups. The orificeswithin each group of orifices were arranged into rows parallel to theair flow. The distance between the rows of adjacent groups of orificeswas 6.0 mm.

Adjacent rows of orifices within a group of orifices were spaced 2.0 mm.apart. Within a row, the orifices were spaced 8.0 mm., apart. Within agroup of orifices, orifices in a given row were displaced relative tothe orifices in an adjacent row by half the distance separating theorifices within a row. During the spinning, the lower surface of thespinning plate had a temperature of 276° C. Positioned below thespinnert plate was a blow box assembly. Air at room temperature waspassed through the blow box rear chamber and filter composed of gauze.The air moved through the blow box transversely to the molten filamentsfalling downwardly through the same and flowed parallel to the rows oforifices. The velocity of the air was 34 centimeters per second and thezone through which the filaments were exposed to the air was 100centimeters in length. The quantity of the air was 2275 liters perminute.

The resulting threads were wound and subsequently drawn to form a yarnhaving an average filament denier of 1.56. The denier evenness was 5.5%.

EXAMPLE 8

Additional polymer was spun in an identical manner to Example 7 througha 60 mm. plate except the orifices were all arranged into a single groupas shown in FIG. 9. The resultant threads had a denier evenness of 6.4%.

It will be appreciated that with a spinning plate of the same diameterthe provision of a smaller number of spinning orifices allows thespacing between adjacent orifices to increase thereby promoting moreuniformity in the denier of the filament bundle.

EXAMPLE 9

Additional polymer was spun in a manner similar to Example 8, exceptthat spinning plates with 48 orifices (200μ diameter) were used, onehaving three open lanes (i.e. 4 groups of orifices) and the other havingthe normal or conventional single group of orifices (as shown in FIG.8). The threads obtained from the three lane spinning plate had a totaldenier of 70 and an evenness of 4-5% and the thread from the other platehad the same denier and an evenness of 6%.

It will be appreciated that the spinning plates useful for the purposeof this invention generally will have a circular configuration similarto those conventionally used in the melt spinning of synthetic yarns.However, other configurations are equally suitable for the purposes ofthis invention.

Also, it will be understood from the description of th invention and theillustration of the spinning plates provided in FIGS. 3 through 10 thatthe outermost spinning orifices in each group are spaced from theperiphery of the spinning plate at distances varying from 5 to 10 mm.Accordingly, the operative or effective area of the plate whereinspinning orifices are provided is smaller than the area of the spinningplate. Consequently, the density or number of spinning orifices per unitarea is determined by the effective or operative area of the plate.Generally, in accordance with this invention the number of spinningorifices per unit area will be greater than 1.4 holes per cm². Forexample an effective diameter of a plate having a diameter of 60 mm. maybe 50 mm.

It should also be recognized that the density of spinning orifices andthe arrangement of the open lanes or channels determines the relativespacing between the filaments which are extruded downwardly from theplate. It has been determined that the direction of the flow of coolinggas through the filaments is preferably parallel to the open lanes orchannels. However, the cooling gas may enter at an angle to the lanedirection with the eveness of the filaments decreasing as the angleincreases. For this reason it is preferred, as previously noted, thatthe cooling gas enter directly into the channels or lanes.

It has also been found that in accordance with the present inventionthat in the production of filaments having a non-circular cross-section,the modification ratio can be increased by using a spinning plate havingat least one open lane or channel arranged in the manner disclosedherein. Apparently, the improved uniformity of cooling enhances thedesired level of cross-section definition which is measured by themodification ratio.

What is claimed is:
 1. An apparatus for melt spinning of polymers intosynthetic yarns which comprises a spinneret assembly means for extrudingmolten polymer through spinning orifices spaced apart in a spinningplate to form a plurality of filaments and a blow box means, operativelyassociated with said spinneret assembly means, for directing a flow ofcooling gas transversely across the plurality of filaments that extendvertically downward from the spinning plate, the spinning plate havingan operative area wherein at least two groups of a plurality of saidorifices are provided, said groups being arranged to provide at leastone open lane that extends across the operative area of the plate in adirection parallel to the flow of said cooling gas and the lane having awidth greater than the distance between adjacent orifices within each ofsaid groups and the spinning plate having an average of from 2 to 10orifices per (10 mm.)² of the operative area, whereby said plateproduces a yarn of a high filament count and of a low denier perfilament count that exhibits a reduced degree of denier unevenness ascompared with a yarn of the same filament count and denier produced by aconventional spinning plate having the same operative area.
 2. Theapparatus of claim 1, wherein said orifices are arranged in linear rowsthat are parallel to each other and to the direction of flow of thecooling gas across said spinning plate.
 3. The apparatus of claim 1,wherein the adjacent orifices of said plurality of orifices are spacedapart from each other by a distance of at least 1 to 2 mm.
 4. Theapparatus of claim 2, wherein the lane has a width that is from 1.5 to10 times that of the distance between adjacent rows of orifices.
 5. Theapparatus of claim 1, wherein the spinning plate has a diameter from 20to 200 mm.
 6. The apparatus of claim 1, wherein the spinning orificesare circular and have a diameter ranged from 175 to 450μ .
 7. Theapparatus of claim 1, wherein the spinning orifices have a non-circularconfiguration to define filaments having a multilobal cross-section.